Fos licenses early events in stem cell activation promoting skeletal muscle regeneration [RNA-seq]

Muscle stem cells, also known as satellite cells, are largely non-proliferative in uninjured skeletal muscle but transition at sites of injury into rapidly dividing progenitors that mediate muscle repair. As early events in satellite cell activation are rate-limiting for recovery from muscle damage, there is substantial interest in discovering their molecular driver(s). Using a comparative transcriptomic approach, we identified a prominent Fos signature in recently activated muscle satellite cells, which was rapidly and transiently induced by muscle damage. Functional interrogation using complementary genetic mouse models revealed that FOS is required for efficiently initiating key stem cell functions, including cell cycle entry, stem/progenitor cell expansion, and regeneration of muscle after injury. Transcriptional profiling further revealed that FOS activates critical gene circuits that stimulate cell migration, proliferation, and differentiation­ while simultaneously repressing quiescence-promoting gene signatures. Pharmacological and genetic disruption of one of these FOS-activated target genes, mono-ADP Ribosyl-Transferase 1 (Art1), in freshly isolated satellite cells substantially diminished cell cycle entry and expansion of the pool of regenerative stem cells. Together, these data implicate FOS as a crucial inducer of early-acting, pro-regenerative gene targets and highlight new transcriptional and post-translational modification events necessary for optimal injury-activated muscle stem cell regenerative responses. RNA-Seq dataset 1: Fresh SCs were isolated via FACS from resting skeletal muscle (hind-limbs, pectoral, and triceps) of 4-month old FosGFP animals (n=4 mice). RNA was extracted from 1000 FosGFP+/B1-Integrin+/CXCR4+/CD45-/CD31-/CD11b-/Ter119-/Sca1- Fresh SCs and 1000 FosGFP-/B1-Integrin+/CXCR4+/CD45-/CD31-/CD11b-/Ter119-/Sca1- Fresh SCs (Samples 1-8). RNA-Seq data set 2: Fresh SCs were isolated via FACS from resting skeletal muscle (hind-limbs, pectoral, and triceps) of 6-month old FoscKO and Control animals (n=3 mice). RNA was extracted from 1000 FosGFP+/B1-Integrin+/CXCR4+/CD45-/CD31-/CD11b-/Ter119-/Sca1- Fresh SCs and 1000 FosGFP+/B1-Integrin+/CXCR4+/CD45-/CD31-/CD11b-/Ter119-/Sca1- Fresh SCs (Samples 9-14).